Computer games often make use of large numbers of bitmap images, such as various backdrop images or individual frames of an animation. Game development tools commonly apply an optimisation where they place multiple individual images on to a single large image without any overlaps. The larger combined image is commonly referred to as a texture atlas or (as in this document) a spritesheet.
Spritesheets are commonly used in the games industry. However, their use typically requires one-off pre- or post-processing steps at either the project load or build points. For example a spritesheet may be prepared, and then imported in its entirety to a game. Alternatively a game may be designed using many individual images, and then arrange these on to spritesheets at build time. Each of these approaches has shortcomings for a game editor that allows the user to make changes and displays their results to them in real-time.
Importing pre-processed spritesheets can be inconvenient to edit. Making an alteration requires changing the source image and then repeating the manual pre-process and import steps. Depending on the tool, further changes may be required to indicate the new locations of images on the spritesheet, or if whole spritesheets were added or removed as a consequence of the change.
Post-processing spritesheets means the editor loses all of the efficiency benefits of spritesheets, because it processes individual images until the user builds the game. This means the editor may use more memory, run more slowly, hit system limits, compress data less efficiently, and take longer to load. It also means the build step must process all of the spritesheets, which can take some time and slow down the user's testing workflow. In some circumstances spritesheets can also render differently to individual images. For example on some graphics hardware mipmaps may be enabled with a POT spritesheet, but not with a NPOT individual image. Therefore stretching an image smaller than its original size could be displayed with a different quality in the editor compared to the built game, which is misleading for the developer.